A present conventional spinning plant uses fibrous material in the form of bales as the feed material and converts it into yarn over a series of various processing stages. The yarn must fulfill predefined quality specifications. The ability to control the conversion automatically is one object of the invention, as will be discussed below. For various reasons this is a very difficult task, of which only some categories of such shall be mentioned below:
There are the various requirements that the product of the spinning mill (yarn) has to fulfill by its further processing to a final product (e.g. a product made from woven or knitted fabric). PA0 There is the number of processing stages that have a decisive influence on the conversion of the fibrous material to yarn. PA0 There are the various technological factors that have an impact on each processing stage.
It has been proposed to divide the spinning line into "areas" that are each attributed to an own process control computer, whereby various divisions have been proposed by various persons (see also DE-A-39 24 779, Maschinenfabrik Rieter AG, and DE-A-39 06 508, Murata Kikai K. K.).
It has also been proposed to combine by way of control the first processing stages of the spinning line (the blow room and the carding room), i.e. DE-A-32 37 864, EP-A-0 303 023 and U.S. Pat. No. 4 876 769. Proposals have been submitted which allow controlling both the composition of the material to be processed as well as the processing of said material in the first stages of the spinning line, i.e. EP-A-0 362 538; EP-A-0 402 940, EP-A-0 399 315 and EP 90 810454.0.
It is still common practice to monitor the evenness of the product of the card (card silver) and to control the card in such a manner that either the best possible or predetermined evenness of the card sliver is achieved (see, for example, U.S. Pat. No. 4,271,565).
Data transmission systems are also presently used for connecting the spinning line or its controls with an overlaid process control system. For further details refer to the Swiss patent application No. 189/91 of Jan. 23, 1991 (lectures of Messrs. Dr. U. Meyer and H. Howald on the occasion of the VDI annual meeting in Aachen on Jan. 30 and 31, 1991). The first plans for realizing such a process control system in the Spinning mill rather aimed at an essential improvement in operational support than "fully automatic operation"; see PCT patent application No. PCT/CH 91/0097 of Apr. 23, 1991.
The efforts of various firms which are active in this field of technology mainly aim at connecting the above-mentioned first stages and the last stages (end spinning and roving yarn stages) of the spinning line and the subsequent bobbin winding machine (for ring-spun yarn) with the process control system; see. EP-A 0 365 901. However, between these first and last stages there are still some other processing stages that fulfill important tasks in processing the material and that are able to supply important information to the process control system.